Development of ion control system of nutrient solutions for preservation of environment and high quality production

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A computer software program for aiding the mixture of macronutrients in nutrient solutions, named "IonAdjuster", has been developed to select the best combination from various nutrient sources to determine required addition rates, according to user-specified demand and current analysis results. "IonAdjuster" determines the quantity of concentrated stock solution to be added from differences in required composition and the present macronutrient concentrations in solution. In practical hydroponic culture of fruit vegetables, fluctuation of ion contents of the solution was decreased and the percentage of top-grade fruit increased by the nutrient stock addition according to "IonAdjuster". On the contrary, in the traditional EC control method, each ion concentration greatly fluctuated, this meant it shifted considerably from the initial value in the later stage of cultivation, and the ionic balance also collapsed. The value of pH decreased gradually as usual in the nutrient solution culture, however, adding the pH stabilization routine to the ion concentration control method could solve it. It was assumed that the combination of "IonAdjuster" and automatic ion sensing, might allow for appropriate and continuous control of solutions in closed hydroponics. This developed system may result in higher crop production, more efficient use of fertilizer and environmental loading reduction by decreasing waster nutrient solution at renewal from open hydroponic systems.